JPH0831449B2 - Material Removal Equipment Using Confined Plasma Etching - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method and apparatus for confining a radio frequency (RF) excited plasma.
RF, in particular in which the non-uniformity of the substrate surface can be corrected
A method and apparatus for confining an excited plasma to a localized, well-defined area of an etchable substrate. The present invention provides a means of shaping the surface of a substrate with great precision and is particularly suitable for forming thin, uniform substrate layers.

[0002]

Conventional processes for shaping the surface of a substrate, especially thinning and shaping surfaces and thin films such as silicon on insulator (SOI), are often mechanical polishing, sputtering, sandblasting, and ion beam bombardment. Method is used. Each of these prior art techniques typically has inherent processing limitations. Chemomechanical processes such as thinning, polishing, and planarization are contact methods where sub-surfaces leave contaminants that can damage the substrate. Plasma-assisted chemical etching methods have been improved over conventional methods such as chemical mechanical thinning in that they reduce the likelihood of sub-surface damage because such plasma methods are non-contact. Moreover, chemical mechanical methods have limited ability to modify the thickness profile of thin films. This is because the ability to change the thin film profile is defined by the planarization of the underlying surface. On the other hand, the plasma method of the present invention can locally remove material depending on the thickness of the thin film measured without contact with the substrate. Therefore, non-contact etching methods such as plasma etching methods reduce the likelihood of sub-surface damage of the substrate.

For optical shaping, plasma-assisted chemical etching methods are superior to conventional mechanical methods in that aspherical surfaces can be shaped as easily as spherical surfaces. That is, since the removal rate is fast, the molding as well as the final molding error correction can be easily performed, the material removal is non-contact, does not damage the sub-surface, and the surface roughness is smoothed by the material removal. It A method of forming by plasma assisted chemical etching, particularly molding of optical elements is disclosed in US Pat. No. 4,668,366.

[0004]

This patent discloses a method and apparatus for shaping a surface by plasma-assisted chemical transfer by mounting it on a surface for treatment to the electrodes of a parallel plate RF driven reactor. ing.
The method disclosed therein controls the removal rate of different areas of the surface by passing a reactive gas through a chamber in the presence of an RF electric field and moving an electrode of relatively small surface area on the surface to be treated. To do. The time that the small electrode spends in each region affects the etching of the surface in that region. However, as described below, the devices and methods described herein lack the means to accurately control the profile or shape of the material removal footprint. Such means are necessary when accurate error correction of the surface is desired. The present invention provides a means of controlling the profile of the material removal footprint. It is an object of the present invention to provide a means of confining an RF excited plasma to a well defined area. Another object of the present invention is to provide a non-contact material removal tool that can be accurately scanned on a substrate surface. Another object of the invention is to provide a means for controlling the properties of the etching process method so as not to damage the sub-surface. Another object of the invention is to provide a means for optical element molding. Another object of the invention is to provide a means for controlling the thin film thickness profile. Another object of the present invention is to
The purpose is to provide a means for precisely smoothing the surface of the substrate.

[0005]

The present invention provides a high frequency (R
F) A material removal apparatus utilizing plasma etching to shape and thin the surface by accurately confining the excited plasma locally to a well defined region of the substrate.
SUMMARY OF THE INVENTION The present invention is a material removal apparatus comprising a reactor for performing a confined plasma assisted chemical etching reaction on the surface of a substrate, a container and a localized area of the substrate disposed within the container. A first dielectric insulator defining a plasma chamber cavity for performing a local plasma etching reaction, a means for supplying a reactive gas flow to the plasma chamber cavity, and a high frequency power for generating plasma in the plasma chamber cavity. Means for supplying the reaction gas in the plasma chamber cavity,
A second dielectric insulator disposed in the container and surrounding the outer periphery of the first dielectric insulator, means for supporting the substrate, and means for adjusting the position of the plasma chamber cavity with respect to the surface of the substrate. A second dielectric insulator extends outwardly from the first dielectric insulator proximate to the substrate surface to facilitate extinction of the plasma outside the plasma chamber cavity, and local plasma etching is performed. The end of the first dielectric insulator facing the substrate has a second dielectric insulator facing the surface of the substrate so that the plasma density becomes high and the conduction of the reaction gas flow decreases in the region adjacent to the position where it is performed. Is projected from the surface of the substrate in the direction of the substrate by a predetermined distance. With such a configuration, the plasma emission means is not in physical contact with the substrate, the substrate material can be removed at a high speed by plasma etching, and the substrate material removal rate and the spatial removal shape are sufficient. It can be controlled in a predictable manner, and the confined plasma can move over the surface of the substrate.

Accurate confinement of the RF-excited plasma limits the field supply area and limits the reaction gas pressure to the area where a given peak RF field only allows plasma breakdown locally, supporting the discharge. The discharge is carried out by filling the undesired regions with a solid insulator by selecting the constituents of the reaction gas such that the diffusion of electrons is locally restricted.

Repeatable etch rate, spatial distribution,
And the generation of the inventive feature of the precise confinement of the inventive RF excited plasma is useful non-contact material removal used as an optical shaping device, a thin film thickness profiler, or an accurate planarization or smoothing device. Providing tools. The present invention provides a means of shaping high quality optical surfaces, including aspherical surfaces that are difficult to manufacture by conventional methods. The present invention also provides a means for manufacturing silicon on insulator (SOI) wafers and structures, and for processing uniform, smooth, and undamaged substrates for semiconductor device fabrication.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a non-contact etchable material removal tool for shaping the surface of an etchable substrate. Referring to FIG. 1, a device for confining a plasma etching region on a substrate comprises a reactor 10 designed to transfer a reaction gas to a region on the surface of the substrate where an RF electric field is provided. Reactor to obtain the desired result
10 has a plasma chamber 14 with a wall 15 bounded by a first dielectric insulator 16 and a ceiling 18 bounded by a reactive gas diffuser 20. Since the plasma chamber 14 is the center of the etching reaction, the first dielectric insulator 16 must be a non-contaminated material. Above the chamber 14,
The RF drive electrode 22 is fixed between the diffuser 18 and the first dielectric insulator 16. A reactive gas supply pipe 24 passing through the center of the first dielectric insulator 16 supplies a reactive gas to the diffuser 20 in the plasma chamber 14 during the etching operation. The RF input conductor 26 connects the RF drive electrode 22 to the RF field power supply. Second
The dielectric insulator 28 surrounds the first dielectric insulator 16, substantially covers the substrate 12, and is sized sufficiently to not form a plasma outside the chamber 14. The components of the reactor 10 are the first set of walls extending from the base 34 to the intermediate ceiling 36.
32 and a second set of walls 38 extending to the upper ceiling flange 40
It is housed in a vacuum container 30 composed of.

In operation, a vacuum is obtained by evacuating through a vacuum outlet 42 at the bottom of vacuum vessel 30. During etching, the etchable substrate 12 located below and adjacent to the plasma chamber 14 is supported by a substrate holder 44 which also acts as a second electrode, which preferably has a potential at ground.

Substrate holder 44 allows the precise placement of localized etching reactions on the surface of substrate 12 in XY.
It is attached to the position setting table 46. The reactor 10 has means 48 for adjusting the distance between the plasma chamber 14 and the surface of the substrate 12. The reactor 10 also comprises means 50 for adjusting the angle of the terminal end 52 of the plasma chamber 14 with respect to the surface of the substrate 12.
Although the embodiments described above provide a means for positioning the plasma chamber 14 with respect to the surface of the substrate 12, other variations such as permanently fixing the plasma chamber assembly and positioning the substrate in multiple dimensions are readily substituted. Can be done.

The bellows 54 mounted between the ceiling flange 40 of the vacuum container 36 and the second dielectric insulator 28 is the reactor 10.
Form a means for vacuum-sealing the plasma chamber 14 in the reactor.
Allow relative movement within 10. A plurality of observation ports 56 are provided for observation of the reaction device 10.

The basic etching operation of the plasma assisted chemical etching reactor 10 is described by Zarowin in US Pat.
No. 366. However, this patent specification does not disclose means for locally confining the plasma to the surface of the substrate whose material removal profile can be controlled.

The confinement of plasma etching to local areas according to the present invention limits the area of application of the RF field and places the reaction gas pressure on the area where a given peak RF field allows only local plasma breakdown. It can be done by selecting the components of the reaction gas so that the diffusion of the electrons that limit and support the discharge is locally limited, and fill the reactor capacity with a solid insulator whenever discharge is not desired. . The reactor 10 shown in FIG. 1 is designed to use one or more of these different containment techniques.

Confinement of the plasma etch region by RF field limitation is established by supplying RF energy to the region that is well enclosed by the insulating container. FIG.
Referring to, the insulating container is "error" with respect to the substrate 12.
A plasma chamber 14 configured to have an opening when placed close to the etched surface characteristics of the dimensions of the enclosed plasma removal tool required for correction. In order to generate plasma, the depth of plasma chamber 14 must be much longer than the Debye length. The plasma method investigated according to the present invention has a Debye length of about 1 mm. A gap is maintained between the terminal end 52 of the plasma chamber 14 and the substrate 12 during the etching operation. Terminal end 52 of plasma chamber 14
Does not contact the substrate 12. In fact, the gap can vary between 0.25 and 10 mm.

Another limitation of the electric field is the RF drive electrodes 22 and R.
This can be done by appropriately limiting the size of the F-drive diffuser 20. The use of small electrodes having a diameter approximately equal to the diameter of the plasma chamber 14 effectively achieves a confined, intense local plasma at the surface where the plasma etching takes place. Since it is important to limit the size or conductive extension of electrode 22, the electrode does not extend beyond plasma chamber wall 15. RF located adjacent to and below electrode 22
The drive gas diffuser 20 is also dimensioned so that it does not extend below the wall 15. This is because the diffuser is composed of a material that is electrically conductive and porous, and the diffuser is part of the RF circuit. The diffuser has two functions. The first is a function of diffusing the reaction gas into the plasma chamber, and the second is a function of providing an RF excitation electric field inside the plasma chamber 14 as an extension of the RF electrode. In particular, porous silicon carbide and graphite electrodes have been successfully used as diffuser materials.

The size of the plasma chamber 14 is appropriately determined, and the RF
In addition to limiting the dimensions of electrode 22 and diffuser 20, the RF field can be limited by the use of additional dielectric material. In addition to the first dielectric insulator 16 used as the wall 15 of the plasma chamber 14, the second dielectric insulator 28 is located in the reactor 10 so that the first dielectric insulator 16 is It surrounds and essentially covers the entire surface of the substrate 12. The second dielectric insulator 28 primarily fills the reactor capacity in regions where plasma discharge is not desired by the solid insulator. This capacity of filling the reactor 10 with the second insulator 28 has two effects. First, the insulator removes the reactive gas from areas where plasma discharge is not desired, i.e., areas adjacent to the footprint of the local plasma etch area. Second, the insulator provides a very high impedance path to all conductive surfaces associated with the etching path (the path between the RF drive electrode 22, the substrate 12 in the local plasma region, and the substrate holding electrode 44). Is. Therefore, the area of application of the RF field and plasma where etching is desired is limited. This localized plasma generation ensures that the footprint of the removal tool is accurate.

In the preferred embodiment of the invention, the plasma chamber has a diameter of 0.5 inches. However, the diameter of the plasma chamber can be varied to accommodate the footprint of the removal tool needed to achieve the desired error correction.

The plasma etch region can also be locally confined by limiting the reaction gas pressure to a region where the RF field allows only local plasma breakdown. This can be achieved by supplying the reaction gas to the reaction gas supply pipe 24. Reaction gas supply pipe 24
Sends the reaction gas directly into the plasma chamber 14 by the diffuser 20. The reactive gas exits the plasma chamber and etching location through a high flow impedance region defined by an opening between the terminal end 52 of the plasma chamber 14 and the substrate surface,
It flows into the low flow rate impedance region 39. The low flow impedance region 39 is evacuated by a vacuum pump (not shown) so that the pressure outside the plasma chamber 14 is much lower than the pressure inside the chamber. After the RF discharge is initiated, the plasma region is provided with a low impedance path, thus blocking the etching reaction outside the region of the footprint.

By careful selection of the components of the reaction gas, the diffusion of the electrons supporting the discharge can be locally limited and the etching region can be further confined. A gas with a large negative charge attaches to free electrons more rapidly than a gas with a small negative charge. The use of a highly negatively charged gas reduces the number and mobility of free electrons available for etching, thus reducing its average energy and reducing the likelihood of reactions outside plasma chamber 14.

As mentioned previously, the gap between plasma chamber 14 and substrate 12 can be varied by several means. For many applications it is not possible to maintain a gap less than the plasma Debye length, ie the length that prevents the plasma from diffusing outside the chamber region. Therefore, by using a reaction gas with a very high negative charge, the plasma is confined for high etch rates and the gap is debye length (about 2 m).
longer than m). In some applications, a small percentage (about 5%) of negatively charged gas is sufficient to provide a well-confined plasma. Sulfur hexafluoride and nitrogen trifluoride are known negatively charged gases with a sufficient negative charge,
It is useful for confining the plasma etching area.

Therefore, by applying the above-mentioned principle of confining the plasma etching region, a controlled localized etching can be used, and the localized plasma material removal will result in a programmed correction to the substrate surface. It can be carried out. The programmed correction is performed by moving the position of the substrate area under the plasma chamber 14 to be corrected. The movement of the substrate 12 in the orthogonal direction with respect to the plasma chamber is performed by moving the XY position setting table 46 accordingly. Figure 2 (a)
Referring to (c), the plasma etching material removal profile can be changed by changing the gap between the plasma chamber 14 and the substrate 12. When the gap is small, for example 0.5 mm, the profile tends to have edges extending vertically to the floor. The radius of curvature of the profile at the point where the edge connects to the floor cannot be less than the Debye length due to physical limitations of the plasma. When the gap is large, for example 3 mm, a larger Gaussian profile can be maintained. Referring to FIG. 3, for a given set of plasma parameters (reaction RF frequency, RF power, pressure, and reaction gas composition) and a given gap, the material removal profile is controllable and repeatable.

Therefore, it can be appreciated that the present invention provides a means for accurately molding a substrate. The present invention is ideally adapted to aspherical surfaces that are difficult to manufacture by conventional methods. The present invention further includes SOI
It provides a new means of manufacturing wafers and structures and processing uniform, thin, flat, smooth and undamaged crystalline substrates for the manufacture of various types of semiconductor devices.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a reactor capable of confining a plasma etching region to a localized region of a substrate.

FIG. 2 shows that when the gap between the substrate and the plasma chamber is greater than and approximately equal to the plasma sheath width,
And a graph showing the profile of the etching respectively formed when it is smaller than that.

FIG. 3 is a graph showing a comparison of etching profiles when different plasma etching properties are used according to the present invention.

[Explanation of symbols]

10 ... Reactor, 12 ... Substrate, 14 ... Plasma chamber, 16, 28 ... Dielectric insulator, 20 ... Diffuser, 30 ... Vessel, 46 ... XY position setting table.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-4-212253 (JP, A) JP-A-4-242924 (JP, A)

Claims (11)

[Claims] 1. A reactor is provided.ThenSubstrate surfaceAboveContainment
Plasma-assisted chemical etching reactionDoMaterial removal
LeavingapparatusAtContainer and Located in this container, local to the local area of the substrate
To perform plasma etching reaction Plasma chamber cavity
To limitA first dielectric insulator,  Supplying reactive gas flow to plasma chamber cavityMeans to do High frequency to generate plasma in the plasma chamber cavity
 Means for supplying power to the reaction gas in the plasma chamber cavity
When, Located within the vessel and defining the plasma chamber cavity
The second dielectric insulator surrounding the outer periphery of the first dielectric insulator
A curb, Means for supporting the substrate, For the surface of the substrate Adjust the position of the plasma chamber cavity
Means toBe equipped with The second dielectric insulator is outside the plasma chamber cavity.
To induce the extinction of plasma in
Extends outward from the electrical insulator close to the substrate surface, Area adjacent to the location where local plasma etching is performed
Plasma density is high and reaction gas flow conduction is low
The end of the first dielectric insulator facing the base as
Is the surface of the second dielectric insulator facing the surface of the substrate.
Project a predetermined distance in the direction of the base This
Material removal characterized by andapparatus. 2. A means for supplying high-frequency power comprises a first electrode arranged in a plasma chamber cavity and a conductive gas expansion means.
And dispersion device, and a second electrode which is located outside of the plasma chamber cavity, the substrate first electrode and a second to complete the electrical circuit for supplying a high-frequency power to the reaction gas in the plasma chamber cavity
Material removal according to claim 1, wherein the material removal is located between the electrodes of
Equipment . Wherein an upper surface of said first electrode is in contact with the ceiling surface of the plasma chamber cavity, on <br/> surface of the conductive gas diffuser is in contact with the lower surface of the first electrode and that the material removal device according to claim 2. Top and bottom surfaces according to claim 4, wherein the first electrode is substantially the same area, Ho and ceiling shape before Symbol plasma chamber cavity
URN material removal device according to claim 3, wherein has the same flat shape. 5. The top and bottom of the conductive gas diffuser.
The surface has almost the same area and the ceiling of the plasma chamber cavity is
The material removing member according to claim 3, wherein the material has a planar shape that is substantially the same as the shape.
Leaving device. 6. The second electrode is maintained substantially at ground potential.
The material removing apparatus according to claim 2, which is provided . 7. The conductive gas diffuser is porous silicon.
Material removal according to claim 2, which is composed of carbide.
apparatus. 8. The conductive gas diffuser is graphite.
The material removing device according to claim 2, wherein the material removing device comprises: 9. The material removing apparatus according to claim 1, wherein the means for adjusting the position of the plasma chamber cavity with respect to the surface of the substrate is an XY position setting table for adjusting the position in the orthogonal direction.
Equipment . 10. The container contains reaction product and excess reaction product.
Means to evacuate and evacuate the container to remove reactive gas
The material removing device according to claim 1, further comprising: 11. A reactor is provided.ThenSubstrate surfaceAboveClosed
The included plasma-assisted chemical etching reactionDomaterial
RemovalapparatusAt the station including means for controlling the temperature and pressure of the environment within the container
Plasma etching reactionDoContainer means,Placed in a container, Localized area of substrateAgainstStation
Plasma etching reactionTo doPlasma chambercavity
To limitRu first1 Dielectric insulator and gas diffusercavitySupply to
Means to doHigh frequency to generate plasma Power empty plasma chamber
Means for supplying reaction gas in the caveAndEmpty plasma chamber
Conductive with the first electrode placed in the sinusSexualGas diffuser
And, and outside the plasma chamber cavityDepartmentSecond power station located at
The polesHigh-frequency power supply means provided, The above In the containerPlaced,Surround the first dielectric insulator
The placed second dielectric insulator, means for supporting the substrate, and the position of the surface of the substrate in an orthogonal direction with respect to the plasma chamber.
X-Y position setting table meansBe equipped with The substrate supplies high frequency power to the reaction gas in the plasma chamber cavity.
Between the first electrode and the second electrode to complete the feeding electrical circuit
Placed in The second dielectric insulator is a plug outside the plasma chamber cavity.
Outside the first dielectric insulator to promote the disappearance of the zuma
Sideways and adjacent to the area where plasma etching occurs.
Plasma density is high and the reaction gas
A region with high impedance to the flow is generated and
The first dielectric insulator so that the plasma on the side is extinguished
Extends a shorter distance toward the substrate surface
A material removing device characterized in that